Then from these 3 leagues select only 4 teams you will follow in each league:

Example:
ENGLAND PREMIER LEAGUE:

Manchester united

Chelsea

Arsenal

Tottenham

SPAIN LA LIGA:

Real Madrid

Barcelona

Valencia

Sevilla

GERMANY BUNDESLIGA:

Bayern Munich

Schalke 04

Dortmund

Mainz

Once you have selected your 12 teams do not even look at other games or teams!
Remember these are your teams, you have to study them as thoroughly as possible!
It would be impossible to study all teams and leagues properly, that's why I recommend to focus on 3 leagues / 12 teams.

How to study:

1. Form:
Look for "form" in the team. How many games have they won in their last 3 matches? How many goals have they scored?
If a team is in form, and they keep scoring goals, select them in your bet.
Remember that home field advantage is a huge advantage too. So be careful!

2. Do not play teams wich have champions league games the following week! (DO NOT!)
E.g. if Real Madrid play a league game on saturday, and have a Champions league game on the following tuesday, leave Real Madrid out of your bet.

Teams in the champions league tend to rest their star players in preceding league games to be 100% strong for the Champions League games as it is a highly regarded cup competition.
Look somewhere else in your team list.
Ever wondered how a big team like Man united loses to a smaller team with high odds?
Or why Real Madrid loses to Athletic Bilbao?
99.9% of the time in those cases they are resting players for Champions League matches the following week. So be careful!

3. Study your teams injuries!
Are their star players injured?
E.g. Rooney has an ankle injury, so he is out of this week's game ... Will his substitute be as good?
How many other injuries are there in the team? In the defence and offence. Very important!

4. Look at the table standings:
E.g. if Barcelona are 1st in the league table and Real Madrid second with 2 points behind, you know Real madrid is going to fight for those 3 valuable points in their next league game,
and Barcelona will fight harder in their next game, to stay on top.

You need to be on top of all these things to make serious money!!
So I hope you have an idea of how to bet properly.

Last tip:
Do not bet on the following leagues:
Italian serie A and B, Russian Premier League or any smaller league teams they are sometimes linked to match fixing as they get paid huge amounts of money to lose games.